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The 'B' Word: The Future of Spatial Audio on Bluetooth

by Maia Hansen VP of Engineering

Spatial audio is the hottest trend on the block, and High Fidelity's Spatial Audio API is leading the way in quality, experience, and clarity. From Apple to Zoom, companies are beginning to see the benefits of spatial audio and how it can improve user experiences and make remote interactions just plain fun.

However, there's an elephant in the spatial audio room, and its name is Bluetooth. Remote interactions involve not just listening, but also speaking. The biggest challenge with Bluetooth devices today is that the hardware simply can not receive stereo audio and transmit microphone input at the same time. When in listen-only mode, devices can use the full Bluetooth bandwidth to transmit multi-channel stereo audio data; but, when both listening and using the microphone, they have to split the bandwidth between mic and output. This means that when you're using your AirPods or other Bluetooth headset, you can't listen in stereo and use the Bluetooth device to capture your microphone input as well. (It's worth noting, however, that you can often use a different microphone, such as the one built into your phone's handset. Give it a shot at our demo site!)

So does that mean that lack of stereo when using full-duplex Bluetooth is a death knell for spatial audio? Not by a long shot. Spatial audio still has two big things going for it: audio clarity and human ingenuity. 

Audio Clarity

First off, you don't actually need stereo sound in order to experience many of the benefits of spatial audio. In terms of clarity, with High Fidelity's spatial audio, you're not just getting the simplistic left-right panning that other companies call "spatialization." You get a comprehensive fully 3D spatialized acoustic experience that includes real-world attenuation, high frequency rolloff, and an exceptionally low latency head-related transfer function. This leads to extraordinary clarity and understandability, even when the output gets down-mixed to mono by an old-skool Bluetooth device. (We've heard many people who are listening to our demos in mono remark on how powerful the spatialization is, even when they're using a single output speaker or a Bluetooth headset!)

Human Ingenuity

Secondly, we believe that 2021 is the last year that any of us will have to deal with these Bluetooth limitations — and we're not just saying that because it's the right answer for spatial audio. Humans are simply not going to put up with it, especially given the explosion over the past year in our needs and expectations around remote communication. For the rest of this article, we'll be talking about some of the recent advances in Bluetooth technology that, in our estimation, will start to eliminate "The Bluetooth Problem" by the end of 2022 at the latest.

To start with, there's Qualcomm. Qualcomm has an extremely high market share of Bluetooth-related hardware (up to 40-50 percent, depending on who you ask), and its latest technology intends to deliver wired-headset quality on wireless earbuds. The company has already made huge advancements with its aptX Adaptive codecs and TrueWireless Stereo, but recent announcements of Qualcomm’s latest work with Snapdragon Sound indicate that it cares just as much about high quality audio as we do here at High Fidelity. (Forbes has an excellent article providing more details about Snapdragon Sound.) Snapdragon Sound promises to drastically improve data transfer rates between handsets and earbuds, reduce latency, and improve audio quality on voice calls through the use of "super wideband voice." Early adopters, including Xiaomi and Audio-Technica, are expected to bring the first Snapdragon Sound-enabled products to the market in late 2021.

Next, there's research. As all types of wireless technology become more and more de rigeur, companies and academics are working harder and harder to fit as much information into the available radio bands. In addition to the work being done at Qualcomm, researchers around the world have been pushing the envelope of communication efficiency. Advances in technologies such as full duplex radio and multi-user MIMO, as well as 5G and WiFi 6, will directly influence Bluetooth capabilities and specifications. Wireless bandwidth usage is skyrocketing, and as data transmission technologies in general become more efficient and widespread, Bluetooth data transfer — and therefore audio transmission — will adapt to take advantage of new discoveries as well.

This trend is already appearing in the latest core Bluetooth specification, Bluetooth 5.2, and its upcoming Bluetooth LE Audio standard. Bluetooth Core 5.2 has introduced a new audio codec that provides high quality at lower data rates, as well as providing for synchronized data transfer directly to left and right earbuds, and bi-directional data transfer when mics are involved. (This post provides an excellent overview of the highlights of Bluetooth 5.2.) With the latest spec they're also laying the groundwork for Bluetooth LE Audio, which promises to transmit high-quality audio while drawing significantly less power than before. It's not yet clear whether or not Bluetooth will add a mandatory full-duplex stereo profile along with this, but it's just a matter of time before that's available and the Stereo-on-Bluetooth Problem is gone for good.

So what does this all mean for the thousand-pound gorilla, Apple, and their AirPods and headphone-jack-less iPhones? In short, they're going to be experiencing some significant evolutionary pressure around audio quality. We're already seeing them react to this with their advertising for the AirPods Pro and Max, which plays up the company's excellent noise cancellation technology. However, it won't be long before consumers realize that the disadvantages of Bluetooth audio are even more apparent when there's less background noise to mask it! Apple already extends the core Bluetooth stack for iOS-to-AirPod connections, and they use their own codec, so between Apple's market cap and the new BT LE Audio standard, we expect to see them come out swinging as soon as Qualcomm's Snapdragon Sound starts appearing in consumers' pockets and ears.

In summary, Bluetooth has nowhere to go but up. In our estimation, the first consumer Bluetooth devices with support for full-duplex transmission using stereo audio will be available by early 2022 at the latest. And High Fidelity's high quality, low latency, clear and understandable spatial audio technology (and your applications that use it) will be ready to take full advantage of the next generation of Bluetooth!

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Published by Maia Hansen May 4, 2021
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